Ionization chamber with recessed radioactive body

ABSTRACT

An improved chamber assembly for an ionization smoke detector. The chamber assembly includes a cup shaped electrode having attached therein a radioactive source to provide the ionization in the chamber. The radioactive body which is retained in a rivet head container, or the like, is staked to the interior surface of the cup shaped electrode, and to make sure that the radioactive source or its container does not project out into the chamber area, the mounting point of the electrode is dimpled so that the face of the mounted radioactive rivet is substantially flush with the general contour of the interior surface of the electrode.

United States Patent 1 [191 Larsen et al.

[451 Nov. 19, 1974 IONIZATION CHAMBER WITH RECESSED RADIOACTIVE BODY [73] Assignee: Honeywell Inc., Minneapolis, Minn.

[22] Filed: June 22, 1973 [21] Appl. No.: 372,557

[52] US. Cl. 313/54, 250/381 [51] Int. Cl. H01j 7/40 [58] Field of Search 250/381; 313/54; 340/237 S [56] 3 References Cited UNITED STATES PATENTS 2,702,898 2/1955 Meili 250/381 X 3,710,110 1/1973 Lampart et al. 250/381 3,725,011 4/1973 Purt et al. 250/381 X Primary ExaminerArchie R. Borchelt Attorney, Agent, or Firm-Omund R. Dahle [5 7 ABSTRACT An improved chamber assembly for an ionization smoke detector. The chamber assembly includes a cup shaped electrode having attached therein a radioactive source to provide the ionization in the chamber. The radioactive body which is retained in a rivet head container, or the like, is staked to the interior surface of the cup shaped electrode, and to make sure that the radioactive source or its container does not project out into the chamber area, the mounting point of the electrode is dimpled so that the face of the mounted radioactive rivet is substantially flush with the general contour of the interior surface of the electrode.

3 Claims, 2 Drawing Figures IONIZATION CHAMBER WITH RECESSED RADIOACTIVE BODY SUMMARY OF THE INVENTION An improved chamber assembly for an ionization smoke detector. The chamber assembly includes a cup shaped electrode having attached therein a radioactive source to provide the ionization in the chamber. The radioactive source which is retained in a rivet head container, or the like, is staked to the interior surface of the cup shaped electrode, and to make sure that the radioactive source or its container does not project out into the chamber area, the mounting point of the electrode is dimpled so that the face of the mounted radioactive rivet is substantially flush with the general contour of the interior surface of the electrode.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a cross-section of a preferred embodiment of the dual chamber assembly, and

FIG. 2 is an electrical schematic diagram of a circuit utilizing the chamber assembly.

DESCRIPTION Referring now to FIG. 1 there is generally disclosed a dual chamber assembly for an ionization smoke detector. The upper ionization chamber 1 1 is a reference chamber which is nearly sealed and does not freely admit the surroundingair. The lower ionization chamber 12 is the sensing chamber which is designed to freely allow through it circulation of the surrounding air so that when smoke is present in the air it can be rapidly detected. A cup-like electrode 13 defines the reference chamber. A flange 14 extending around the perimeter of the cup electrode 13 serves as a mounting means.

An ionizing body 15 of radioactive material and a mounting member are fastened in the upper surface or section 16 of the electrode 13. In the drawing a specific embodiment of the radioactive material and mounting member is shown in the form of a rivet which has a depression in the rivet head portion into which the radioactive body is placed. The radioactive body may be sealed in with a cover of gold foil through which the radiation occurs. The electrode section 16 has a dimple or recess 17 stamped into the surface so that the encapsulated radioactive body 15, which is mounted in the recess 17, does not extend out into the chamber but instead the radiation surface of the mounting member is substantially flush with the general internal contour of the electrode 13 at the surface 16. The mounting member configuration is not intended to be limited to a rivet but, whatever the exact embodiment of radioactive source and mounting member, the invention is important where the height of the source and/or member causes it to extend out into the chamber area.

Prior to recessing the radioactive source, the encapsulated source extended out into the area of the chamber resulting in a distortion of the electric field within the chamber and a concentration of ion flow to the encapsulated source rather than a uniformly distributed ion flow to a large area of cup electrode 13. The undesired concentration of ion flow prior to this invention had an adverse effect on the primary function of the apparatus, i.e., that of smoke detection. In the improved chamber assembly in which the encapsulated radioactive source has been recessed into the outer well of the chamber such that the radiating surface of the source is flush with the general contour of the cup electrode, a significant improvement in operation resulted.

The sensing chamber 12 is defined by a circular cuplike electrode 13 which is identical to the previously described electrode 13 except that an additional stamping step opens a plurality of louvers 20 to allow the free exchange of the surrounding air into the sensing chamber.

The dual chamber assembly is mounted to a circuit board 21 which has a circular cutout to accomodate the ionization chambers. The reference and sensing chamber are separated by a fluorocarbon (such as Teflon) disc or wafer 22 which forms a non wettable insulating common wall of each chamber. Embedded in the center of wafer 22 is a metallic insert, i.e., an electrically conductive electrode support 23. The conductive insert 23 includes a disc portion 24 and an extension or tail portion 25 extending through the wafer to a connection point 25' at the edge.

The second electrode of the reference chamber 11 is a metal disc 27 and it together with an identical part 27 in sensing chamber 12 are both fastened to the offset section of the insert 23. In order to compensate for the thickness of the PC board 21 in the assembly, which would otherwise unbalance the dimensional symmetry of the two chambers, the insert conductor 23 has a sufficient offset in the center mounting portion to achieve dimensional symmetry. This offset raises electrode 27' above the surface of wafer 22. The electrodes 27 and 27' and the conductive mounting means 23 being staked together are all electrically common to each other and the terminal 25 provides for connection of the signal potential at these electrodes to the high impedance signal input terminal of a suitable electrical measuring circuit 30 shown schematically in FIG. 2. A plurality of fastening means 31 through flange 14 secure the assembly together.

The embodiment of the invention in which as exclusive property or right is claimed are defined as follows:

1. In an ionization smoke detector of the type having a smoke sensing chamber containing a radioactive source, an improved chamber assembly comprising in combination:

a cup like electrode mounted on a base member and defining an exterior chamber wall of an ionizing chamber;

a radioactive body for ionizing the area within said chamber, said body being mounted on the cup like electrode;

a dimple like recess in said cup like electrode at the mounting point of said body which is effective to recess the body so the radiating face thereof is substantially flush with the inner surface of the cup like electrode whereby the uniformity of ion flow to the inner surface of the electrode is improved.

2. The invention according to claim 1 in which said dimple like recess whereon said body is mounted is located at the apex of said cup like electrode.

3. The invention according to claim 1 in which said radioactive body is encapsulated in a rivet head of a rivet and in which there is a hold through said electrode at said dimple like recess into which said rivet is mounted. 

1. In an ionization smoke detector of the type having a smoke sensing chamber containing a radioactive source, an improved chamber assembly comprising in combination: a cup like electrode mounted on a base member and defining an exterior chamber wall of an ionizing chamber; a radioactive body for ionizing the area within said chamber, said body being mounted on the cup like electrode; a dimple like recess in said cup like electrode at the mounting point of said body which is effective to recess the body so the radiating face thereof is substantially flush with the inner surface of the cup like electrode whereby the uniformity of ion flow to the inner surface of the electrode is improved.
 2. The invention according to claim 1 in which said dimple like recess whereon said body is mounted is located at the apex of said cup like electrode.
 3. The invention according to claim 1 in which said radioactive body is encapsulated in a rivet head of a rivet and in which there is a hold through said electrode at said dimple like recess into which said rivet is mounted. 